In order to use OTA updates we need to separate read-only data from temporary and read-write files. We assume that everything that can be written is either generated after only after we boot the system, or is stored in /etc. In other words, everything that is generated by "bitbake agl-demo-platform" is either read-only or is stored in /etc.
Read-only data can be stored under '/usr', '/bin', '/sbin' or '/lib', everything in '/opt' is currently just deleted during OTA-enabled image generating process (see respective warnings during the build process). As far as I'm concerned, all (or at least most of) the data that is now installed under '/opt' is actually read-only and it would be nice to move it somewhere under '/usr'.
Of course, I could also move it automatically while generating OTA image, but it will probably break some path variables, so the cleaner way would be to change paths in the recipes.